Method and means of generating gravity waves

ABSTRACT

A method and means of generating a wave pattern in a body of water with a period and magnitude sufficient to sweep pressure type mines comprising the placement and detonation of a plurality of small explosive charges in a predetermined space-time relationship.

United States Patent 1191 McGraw Sept. 9, 1975 [54] METHOD AND MEANS OFGENERATING 2,619,186 11/1952 Carlisle 181/5 C GRAVITY WAVES 3,048,2358/1962 ltria 4 4 i Y 1 i 1 181/,5 C 3,262,388 7/1966 McCarty v i i i 1102/18 Inventor: Charles M w, l n a- 3,354,826 ll/l967 Axelson et al.102 22 [73] Assignee: The United States of America as represented thesecretary of the Primary ExaminrVerlin R, Pendegrass Navy WashingtonAttorney, Agent, or FirmL0uis A. Miller; Don D. 22 Filed: Dec. 6, 1967y; il iam Skeer [21] Appl, No; 690,702

[57] ABSTRACT [52] U.S. Cl. .1 102/10; l8l/ll6; 102/22 [51] '3 F42) U06A method and means of generating a wave pattern in 158] held of Search[OZ/l0 22 24; a body of water with a period and magnitude sufficient181/5 C to sweep pressure type mines comprising the placement anddetonation of a plurality of small explosive [56] References C'tedcharges in a predetermined space-time relationship.

UNITED STATES PATENTS 2,320,248 5/1943 Shimek .7 |8l/.5 C 5 Claims, 2Drawing Figures PATENTED 9 975 Fi .1 XL N Fig.2

Charles 7. McGmw INVENTOR.

BY J/ M AGENT METHOD AND MEANS OF GENERATING GRAVITY WAVES The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

This invention relates to the generation of a long period, gravitationalwave in an aqueous medium. More particularly, the invention contemplatesthe generation of a high magnitude gravity wave with a long period whichhas a practicable application as a sweep for pressure-responsive,submarine mines.

A common type of submarine mine is actuated by a pressure variationcaused by the proximity of a moving vessel. This type of mine employs anactuation circuit which is insensitive to short duration pressure variations and other pressure variations not produced by ship movements. Theaforementioned selective sensitivity renders this type mine difficult tosweep by generation of an artificial signal. An economical method ofgenerating signals of a magnitude sufficient to neutralize this type ofmine in a harbor or large open body of water employing low cost andconveniently portable apparatus has awaited the technological advancedevised by applicant and herein fully disclosed.

Accordingly, an object of this invention to provide an improved methodand means for sweeping, destroying, and neutralizing pressure sensitivemarine mines.

Another object of this invention is to provide a method for thegeneration ofa large displacement, long period wave in a body of water.

More particularly, this invention has as its object the generation of alarge amplitude, long period wave in a body of water as means forsweeping pressure type mines.

A further specific object of this invention is to provide a method forthe production of a large amplitude, long period, surface wave in a bodyof water by the timely detonation of spaced explosive charges.

Other objects and many of the attendant advantages will be readilyappreciated as the subject invention becomes better understood byreference to the following detailed description, when considered inconjunction with the accompanying drawings wherein:

FIG. I is a vertical elevation showing the placement of explosivecharges and an idealized hypothetical wave generated thereby;

FIG. 2 is a plan elevation showing the placement of charges to generatea wave to sweep a harbor having a mine field.

Referring to FIGS. 1 and 2, there is shown three explosive charges ll,12, and 13, which are evenly spaced by a distance S and at a depth hbeneath the surface. Assuming the first charge 11 is detonated, asurface disturbance accompanying the detonation will radiateomnidirectionally outward in the familiar concentric pattern. When thissurface disturbance, shown in profile as a damped sine wave 14 having acircular wave front 17 (FIG. 2), approaches the second explosive charge12, it, too, is detonated, such that the wave generated by thedetonation of charge 12 reinforces wave 14 to produce a larger amplitudewave illustrated in profile at 15. This wave continues in the directionof the line of explosive charges as an ever widening wave front 18,until charge 13 is approached. Charge 13 is then timely detonated toprovide reinforcement for the traveling wave to produce a wave having aprofile 16. This wave continues through successive explosivereinforcements until a desired wave form shown at 19 is obtained and thewave continues in its direction of travel until a pressure type mine,shown diagrammatically at 20, is encountered, whereupon detonation ofthe mine occurs.

The direction of travel and extent of the wave front as well as thewaveform are dependent upon the relative positions of the charges, amongother parameters. Thus F108. 1 and 2 shows a three charge generatingarray, wherein all of the charges are at the same depth and in a lineararrangement. While such an arrangement is suitable for illustrativepurposes the actual practice may require other, more complex,arrangements. Thus the second charge may consist of a plurality ofcharges placed equal distance from, and radially oriented with respectto, the first charge. The exact placement is dependent upon the desiredtravel and shaping requirements of the generated wave. In a similarfashion the depth of the charge placement may be varied to accommodatevarious water depths and the wave or pressure profile desired to begenerated. These variations are considered to-be understood equivalentsto one proficient in the fields of hydrokinetics and may be optionallyincorporated in practicing the wave generation method of this invention,if desired.

The pressure type marine mine is sensitive to a particular pressurepattern dependent upon the hull shape and speed of a particular typevessel. Each vessel type has its associated characteristic pressurepattern, termed signature. Generally speaking, each signature ischaracterized by a short duration positive portion, termed bow portion,followed by a long duration negative portion, and terminated by anothershort duration positive portion, termed stern portion. The importantaspect for minesweeping purposes is the reinforcement by successivedetonations of the long period negative portion of the damped sine wavepattern created by a single detonation. The positive portion of thewaveform is likewise reinforced but for mine-sweeping applications thisis less important. While the exact detailed signature for each crafttype is difficult to synthesize a reasonable facsimile of thefundamental frequencies may be generated.

A pressure signature may be synthesized by varying the depth placementand relative positional placement of the individual charges. Ofconsiderble importance is the type of explosive material used, as wellas the size and shape of the charge. The individual effects of eachtype, size, and shape are known parameters to those cognizant of marineordnance, but, because the specifics of such parameters have no directcontribution toward the understanding of the instant invention, thedetails are not included herein. It is noted, however, for purposes ofcompleteness, that one may use, to good effect, a readily availablecharge of RDX explosive material having a mass of approximately 300pounds.

The generation of pressure waves in a fluid medium have many variables,including the density of the fluid as effected by both temperature andsalinity. These variables preclude the synthesis of a pressure signaturebeing an exact science, especially as generated by the use of explosivecharges; thus, the precise placement of charges must be arrived at bysomewhat empirical methods. This provides no great disadvantage inactual use, for such placements may be, once determined, stored intabular form for the limited types of ships for which a minesweepercommander may be expected to provide countermeasure sweeps.

The charges may be secured in position by any of several known methodsor even, if desired, placed on the bottom of the body of water,

The timing of the detonation of the successive individual charges isquite critical if optimum wave reinforcement and profile shaping are tobe obtained. The sequence for timing is given by the formula:

where T is delay in seconds from the detonation of the previous or firstcharge to the detonation of the suc cessive individual charge.

S is the distance to the preceding or first charge in feet.

g is the acceleration of gravity in feet per second per second.

It is the depth in feet of the individual charge. Several methods ofassuring the proper timing interval are available to assure the timelydetonation of the explosive charges either precision clockwork,condition responsive, or remotely triggered detonators may be used, ifdesired, for this purpose.

The charges may be launched or jettisoned by any conventional craftincluding marine craft, both surface and submarine, as well as aircraft,both fixed and rotary wing to timely place the individual charges intheir desired positions. It will be appreciated that, when a surfacevessel, as shown in FIG. 2 is used for placing the charges, the timingof the detonation of the individual charges will be such that thesurface vessel may have time to take up a position where the surfacewill be relatively undisturbed by the action of the charges.

While the invention has been described as a method of generating apressure signature for the sweeping of pressure mines, the ease andefficiency of generating large displacement waves will suggest manyother uses to the experienced craftsman in the fields of hydrody namicsand marine warfare. For example, a wave may be generated to carryamphibious landing and assault vehicles over breastwork type defenses tolaunch an assault at periods of low tide and thereby enhance thesurprise aspects of such a maneuver. The method also has applicabilityto peaceful industrial endeavors such as clearing log-jams, or launchingstrategically placed logs in the timber or pulp wood industries. Thismethod may also be successfully employed in the clearing of beaches, anincreasingly important aspect of hydromechanics, or in the movement oflarge volumes of sand and bottom material as encountered in the clearingof channels or the forming of offshore bars, reefs, etc.

Obviously, other embodiments and modifications of the subject inventionwill readily come to the mind of one skilled in the art having thebenefit of the teachings presented in the foregoing description and thedrawings.

What is claimed is:

l. A method of generating a gravity wave disturbance on the surface ofan aqueous medium of such a magnitude and frequency that it simulatesthe pressure disturbance of said aqueous medium produced by the passageof a marine vehicle therethrough to detonate marine mines located withinsaid aqueous medium, said method comprising the steps of:

positioning a first explosive charge at a predetermined location withrespect to the location of said marine mines and at a predetermineddepth beneath the surface of said aqueous medium;

positioning a predetermined number of additional explosive charges atpredetermined depths within said aqueous medium and between said firstexplosive charge and said marine mines so as to effectively assemble anarray of positioned explosive charges lying in a substantiallyhorizontal configuration and extending outwardly from said firstexplosive charge toward said marine mines;

detonating said first explosive charge, thereby generating a gravitywave surface disturbance which has a displacement associated highpressure period followed by a low pressure period which is of apredetermined time duration and which travels out wardly from thelocation of said first explosive charge toward said marine mines on thesurface of said aqueous medium; and successively detonating selectiveones of said additional explosive charges in a predetermined timerelationship with respect to the detonation of said first explosivecharge as to effect reinforcement of said high pressure disturbance andlengthen the duration of said low pressure period, said timerelationship being predetermined with relation to the distance betweensaid first explosive charge and said selective ones of said additionalexplosive charges and the depth below the surface of said selective onesof said additional charges. 2. A method for generating a gravity wavewithin an aqueous medium which simulates the pressure signature of apredetermined vehicle moving therein for detonating pressure sensitivemarine mines located therein comprising the sequential steps of:

positioning a first explosive charge at a predetermined location withrespect to the location of said pressure sensitive mines and at apredetermined depth beneath the surface of said aqueous medium;

positioning a predetermined number of additional explosive charges atpredetermined depths within said aqueous medium in predeterminedsubstantially horizontal spatial relationships with said first explosivecharge and with each other; detonating said first explosive charge tocreate a gravity wave disturbance in said aqueous medium which radiatesomnidirectionally therefrom; and

successively detonating selective ones of said additional explosivecharges in such timed relationship with respect to the detonation ofsaid first explosive charge as to effect reinforcement of the aforesaidgravity wave disturbance, so as to effectively lengthen the periodthereof along predetermined directions to simulate the pressuresignature of a marine vehicle as said gravity wave radiates within saidaqueous medium the interval between the det onations being determined inaccordance with the expression where T is the delay in seconds from thedetonation of said first charge to the detonation of said additionalexplosive charges,

s is the separation distance expressed in feet from said first charge tosaid additional explosive charges,

3 is the acceleration of gravity expressed in feet per second persecond. and

h is the depth of said selective ones of said additional charges beneaththe surface of said aqueous medium expressed in feet.

3. A method according to claim 1 in which the step of positioning apredetermined number of additional charges includes placing saidadditional charges along charges from a moving surface vehicle.

1. A method of generating a gravity wave disturbance on the surface ofan aqueous medium of such a magnitude and frequency that it simulatesthe pressure disturbance of said aqueous medium produced by the passageof a marine vehicle therethrough to detonate marine mines located withinsaid aqueous medium, said method comprising the steps of: positioning afirst explosive charge at a predetermined location with respect to thelocation of said marine mines and at a predetermined depth beneath thesurface of said aqueous medium; positioning a predetermined number ofadditional explosive charges at predetermined depths within said aqueousmedium and between said first explosive charge and said marine mines soas to effectively assemble an array of positioned explosive chargeslying in a substantially horizontal configuration and extendingoutwardly from said first explosive charge toward said marine mines;detonating said first explosive charge, thereby generating a gravitywave surface disturbance which has a displacement associated highpressure period followed by a low pressure period which is of apredetermined time duration and which travels outwardly from thelocation of said first explosive charge toward said marine mines on thesurface of said aqueous medium; and successively detoNating selectiveones of said additional explosive charges in a predetermined timerelationship with respect to the detonation of said first explosivecharge as to effect reinforcement of said high pressure disturbance andlengthen the duration of said low pressure period, said timerelationship being predetermined with relation to the distance betweensaid first explosive charge and said selective ones of said additionalexplosive charges and the depth below the surface of said selective onesof said additional charges.
 2. A method for generating a gravity wavewithin an aqueous medium which simulates the pressure signature of apredetermined vehicle moving therein for detonating pressure sensitivemarine mines located therein comprising the sequential steps of:positioning a first explosive charge at a predetermined location withrespect to the location of said pressure sensitive mines and at apredetermined depth beneath the surface of said aqueous medium;positioning a predetermined number of additional explosive charges atpredetermined depths within said aqueous medium in predeterminedsubstantially horizontal spatial relationships with said first explosivecharge and with each other; detonating said first explosive charge tocreate a gravity wave disturbance in said aqueous medium which radiatesomnidirectionally therefrom; and successively detonating selective onesof said additional explosive charges in such timed relationship withrespect to the detonation of said first explosive charge as to effectreinforcement of the aforesaid gravity wave disturbance, so as toeffectively lengthen the period thereof along predetermined directionsto simulate the pressure signature of a marine vehicle as said gravitywave radiates within said aqueous medium the interval between thedetonations being determined in accordance with the expression
 3. Amethod according to claim 1 in which the step of positioning apredetermined number of additional charges includes placing saidadditional charges along a substantially horizontal line extending fromthe location of said first charge toward the location of said pressuresensitive marine mines.
 4. A method according to claim 2 in which thestep of positioning a predetermined number of additional chargesincludes submerging the said additional charges to the same depth.
 5. Amethod according to claim 2 in which the step of positioning apredetermined number of additional charges includes positioning saidadditional charges equidistant from one another and said first explosivecharge by timely jettisoning individual ones of said charges from amoving surface vehicle.